Pulsed gas parison cooling method

ABSTRACT

Rapid cooling of molded workpieces such as PET parisons formed in an injection molding machine is provided by a receiver receiving molded workpieces upon ejection from the molding machine, the receiver being transported out of the molding machine to an adjacent position where a cooling head coupled to a source of cooling fluid such as liquid nitrogen directs the fluid toward the surfaces of each workpiece. The cooling head engages and is sealed to the receiver to inhibit the escape of cooling fluid into the atmosphere thereby reducing cost, environmental impact, etc. A cooling program control coupled to the cooling fluid source supplies a discontinuous flow cooling fluid from said source to contact the workpieces only when the cooling head is engaged with and sealed to the receiver. A vacuum unit withdraws cooling fluid from the receiver subsequent to contact between the workpieces and the cooling fluid. The cooling fluid can then recooled and recycled for reuse.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a Division of U.S. patent application Ser. No. 08/095,664, filedJul. 21, 1993, now U.S. Pat. No. 5,338,172, which is application is acontinuation-in-part of U.S. application Ser. No. 07/765,128 filed Sep.25, 1991, now U.S. Pat. No. 5,232,641 which is in turn a divisional ofSer. No. 07/646,071 filed Jan. 25, 1991, now U.S. Pat. No. 5,114,327.

BACKGROUND OF THE INVENTION

This invention relates generally to apparatus for use in conjunctionwith injection molding machines for rapidly cooling work pieces moldedby the molding machine. The invention relates particularly to a methodand apparatus for rapidly cooling injection molding parisons to beemployed in the manufacture of biaxially oriented articles such ascontainers for carbonated beverages and the like.

The manufacture of biaxially oriented containers such as those formedpolyethylene terephthalate (PET), employs an initial step of forming aparison or preform by an injection molding process. The parisons aregenerally in the shape of a hollow cylinder closed at one end and areoften formed in multicavity molds into which plastic material isinjected around a core positioned within each cavity. Generally the coreand cavity are cooled by means of a liquid flowing through channelswithin the walls of the core and cavity thereby cooling the plasticforming the parison to a form-stable shape defined by the core andcavity.

Once the parison is formed and cooling is initiated, the core andparison are removed from the cavity thereby exposing the outer surfaceof the parison to room temperature air. An ejector or stripper mechanismthen strips the parisons from the cores to expose the inside surface ofthe parisons to room temperature air and to free the molding machine toinitiate another molding cycle. As the parisons are stripped from thecores, any contribution by the cores to the form stability of theparisons is also removed thereby freeing the parisons to be modifiedfrom their initially molded shape by outside forces.

In order to reduce this post molding modification of parison shape, itis desirable that the preform be cooled as much as possible therebyenhancing its form stability. The cooling can be enhanced by merelyretaining the molded article in contact with the cooled cavity and corefor an extended period of time thereby allowing additional heat to beextracted from the parison. This has the undesirable affect of extendingthe time for each injection molding cycle thereby reducing the number ofparisons which can be produced in a given unit of time.

In order to enhance the cooling of the parisons, it has been suggestedto provide additional cooling apparatus. In one such apparatus disclosedin U.S. Pat. No. 4,472,131, the parison, while retained on the core rodof the mold, is positioned within a supercooling mold. The outer surfaceof the parison cools either by direct contact with the wall of thesupercooling mold or by cold air passing through an air gap between theouter surface of the parison and the supercooling mold. The coldcompressed air is introduced at a point corresponding to the tip orsprue end of the preform. After passing along the length of the outerwall of the preform, the air escapes through holes located in the moldadjacent to the preform neck ring or thread finish. During the cooling,the parison is retained on the core rod of the initial mold in which theparison was formed. Thus in order that the molding cycle of the moldingmachine may continue, duplicate core rods and shifting mechanisms forthose core rods must be supplied to permit a reasonable production ofparisons in a given unit of time.

In another disclosure of cooling apparatus found in U.S. Pat. No.4,592,719, the parison is removed from the core rod on which it wasformed by a pneumatic grip which draws atmospheric air by suction alongthe length of the parison between the parison outer wall and thepneumatic grip. The grip then removes the parison from the moldingmachine where a second grip is introduced into the interior of theparison. The second grip also causes atmospheric air to be sucked alongthe inner walls of the parison thereby enhancing the cooling of theparison through turbulent contact with a large volume of ambient air.

In accordance with an earlier embodiment of the present invention asdisclosed in U.S. Pat. No. 5,114,327, an apparatus is provided for usewith an injection molding machine which includes a receiver means forreceiving molded work pieces upon ejection of the work pieces from themolding machine. A transporter means is coupled to the receiver meansfor transporting the receiver means relative to the molding machine froma first position within the injection molding machine to a secondposition adjacent to the injection molding machine. A source of coolingfluid is provided together with a directing means for directing thecooling fluid toward the surfaces of each work piece in the receivermeans. A moving means coupled to the directing means moves the directingmeans relative to the receiver means from a disengaged position to anengaged position where the directing means and receiver means areengaged with each other. Sealing means is provided for sealing thedirecting means to the receiver means to restrict any escape of coolingfluid while the directing means and receiver means are engaged with eachother. Sensor means coupled to the source of cooling fluid andresponsive to the relative position of the receiver means and directingmeans releases cooling fluid from the source only when the directingmeans and receiving means are engaged and are sealed by the sealingmeans. A vacuum means is coupled to the receiver means for withdrawingcooling fluid from the receiver means subsequent to contact between thework pieces and the cooling fluid.

One feature of the earlier embodiment of the present invention is theapplication of a continuous flow of cooling fluid to both the internaland the external surfaces of a work piece while it is completelyenclosed. This feature provides the advantage of confining the coolingfluid so as to contact the work piece repeatedly thereby insuring theextraction of a maximum amount of heat from the work piece with theminimum amount of cooled fluid to achieve a high efficiency heatextraction.

While such apparatus speeds the cooling of the parisons to an acceptableform stable temperature in a shorter time than would be experienced bymere contact with ambient air in the absence of such apparatus, furtherreductions in cooling time are desirable which would allow evenadditional increases in parison production from a given molding machine.Thus an object of the present invention is to develop a method andapparatus for reducing the time period of the cooling of the preformsubsequent to injection molding thereby enhancing the productivity ofthe associated injection molding machine.

SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus is provided foruse with an injection molding machine which includes a receiver meansfor receiving molded work pieces upon ejection of the work pieces fromthe molding machine. A transporter means is coupled to the receivermeans for transporting the receiver means relative to the moldingmachine from a first position within the injection molding machine to asecond position adjacent to the injection molding machine. A source ofcooling fluid is provided together with a directing means for directingthe cooling fluid toward the surfaces of each work piece in the receivermeans. A moving means coupled to the directing means moves the directingmeans relative to the receiver means from a disengaged position to anengaged position where the directing means and receiver means areengaged with each other. Sealing means is provided for sealing thedirecting means to the receiver means to restrict any escape of coolingfluid while the directing means and receiver means are engaged with eachother. Sensor means coupled to the source of cooling fluid andresponsive to the relative position of the receiver means and directingmeans releases cooling fluid from the source only when the directingmeans and receiving means are engaged and are sealed by the sealingmeans. The control means includes a program means for programming apulsed delivery of the cooling fluid to the directing means. A vacuummeans is coupled to the receiver means for generally continuouslywithdrawing cooling fluid from the receiver means subsequent to contactbetween the work pieces and the cooling fluid.

One feature of the present invention is the application of adiscontinuous flow of cooling fluid to both the internal and theexternal surfaces of a work piece while it is completely enclosed. Thisfeature provides the surprising advantage of achieving a faster and moreeffective cooling of the work piece than when a continuous flow ofcooling fluid is employed. A surprising advantage is also present asless cooling fluid is used than when a continuous flow is used. Thediscontinuous flow of cooling fluid can be programmed based on the workpiece size and configuration thereby insuring the extraction of amaximum amount of heat from the work piece with the minimum amount ofcooling fluid to achieve a high efficiency heat extraction.

Another feature of the present invention is the employment of atemperature sensing means for sensing the temperature of the work pieceas it is cooled by the cooling fluid. The sensing means can be employedin an alarm circuit to alert a machine operator of incomplete cooling ofa work piece. The sensing means can also be employed in a recordingcircuit to record production conditions for evaluation to achieveoptimization of the process. The sensing means can also be employed as apart of the control system of the machine as a whole and is desirablypositioned in the receiving means and focused on an initially hotterportion of the work piece to ensure sufficient cooling of the entirework piece.

Yet another feature of the present invention is the employment of a sealmeans between the receiver means and the directing means which preventsthe escape of cooling fluid during the cooling process therebypermitting a recycling of the cooling fluid through a vacuum system.This feature has the advantage of permitting the use of fluids which dueto cost, environmental impact, or other factors, might otherwise not befeasible. The preferred cooling fluids to be employed in the presentinvention are liquid nitrogen (N₂) and liquid carbonic (liquid CO₂).

While the invention is hereafter described in connection with theparticular application of the methods and apparatus herein disclosed tothe molding of PET parisons for subsequent manufacture into biaxiallyoriented containers for carbonated beverages and the like, it will beappreciated that the rapid cooling system in accordance with the presentinvention could be employed for work pieces of a character other thanparisons. Additional features and advantages of the invention willbecome apparent to those skilled in the art upon consideration of thefollowing detailed description of a preferred embodiment exemplifyingthe best mode of carrying out the invention as presently perceived. Thedetailed description particularly refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus in accordance with thepresent invention.

FIG. 2 is a sectional detail view of a receiving means in accordancewith the present invention.

FIG. 3 is a sectional detail view of a directing means in accordancewith the present invention.

FIG. 4 is a sectional detail view of a receiving means and a directingmeans with a parison enclosed therebetween, and including a temperaturesensing means for sensing the parison temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An apparatus 10 for use with an injection molding machine 12 is shown inFIG. 1. The injection molding machine 12 is illustrated only in part toprovide an illustrative environment for the apparatus 10. The injectionmolding machine 12 includes an injection unit 14 which acts to supplyplastic in a molten form to a plurality of cavities 16 in cavity unit18. Each cavity 16 in the cavity unit 18 has a corresponding core 20fixed to core unit 22 which moves relative to the cavity unit 18 bymeans of a power actuated toggle system 24 or similar apparatus as isconventional in the industry. The core unit reciprocates in thedirection "A" so that the cavity 16 and cores 20 cooperate to define anessentially closed chamber in which a work piece such as a parison canbe formed. Subsequent to the formation of the parison between core andcavity, the cavity unit moves to the position illustrated in FIG. 1 andthe molded parisons are stripped from the cores 20 by a stripper plate26 as is conventional in the industry.

The apparatus 10 in accordance with the present invention includes areceiver means in the form of a receiver frame 30. The receiver frame 30includes a plurality of chamber elements 32 in a pattern which willpermit the chamber elements to receive the molded parisons as they arestripped from the cores 20 of the injection molding machine 12 bystripper mechanism 26. The receiver frame 30 is suspended from anoverhead track 34 serving to define a pathway along which the receivertravels in the direction "B". A transport mechanism of conventionaldesign including vertical hanger 36 transports the receiver frame 30from a first position within the injection molding machine 12 so thatthe chamber elements 32 are aligned with the cores 20 to a secondposition adjacent to the injection molding machine 12 as shown in FIG.1.

The receiver frame 30 is coupled to the vertical hanger 36 by adischarge unit 38 which is adapted to pivot the receiver frame 30 abouta horizontal axis in the direction of arc "C" so as to unload thecontents of the chamber elements 32 onto conveyer belt 40 or othersimilar conveying means for conveying the parisons from the position ofthe molding machine 12 to a subsequent processing operation. Once theparisons have been removed from the molding machine and prior to theirbeing discharged by discharge unit 38, they are subjected to a coolingfluid such as liquid nitrogen or liquid carbonic taken from source 42.

The source of cooling fluid 42 is connected by flexible conduit 44 to acooling head 46. The cooling head 46 is suspended from track 48 which isperpendicular to track 34 and defines a pathway for movement of thecooling head 46 with respect to the receiver frame 30 when the receiverframe is in the position illustrated in FIG. 1. A moving means ofconventional design including vertical support 50 causes the coolinghead to move in the direction "D" between a disengaged position as shownin FIG. 1 and an engaged position where the cooling head 46 and receiverframe 30 are engaged with each other as shown generally in FIG. 4. Asealing means, not illustrated in FIG. 1, seals the cooling head to thereceiver frame so as to inhibit any escape of cooling fluid while thecooling head and receiver frame are engaged with each other.

A first sensor means 52 which can be in the form of a microswitch orother similar sensor is coupled to the cooling program controller 55 byan appropriate cable 54. The sensor 52 is responsive to the relativeposition of the cooling head 46 and receiver frame 30 so as to permitrelease of cooling fluid from source 42 only when the cooling head 46 issealed to the receiver frame. The cooling program controller 55 controlsthe release of cooling fluid from the source 42 as later described.

A vacuum unit 56 is coupled to the receiver frame 30 by means of anappropriate flexible conduit 58 for withdrawing the cooling fluid fromthe receiver frame 30 subsequent to contact between the cooling fluidand the parisons held within the chamber elements 32. The apparatus 10can include a recycling unit 60 which can include a fluid chiller andpump of conventional design recools the cooling fluid received by thevacuum unit 56 and recycles the cooled and filtered fluid to the source42 for subsequent use. Such a recycling unit 60 is highly desirable ifnot mandatory when employing fluids having significant potential forenvironmental impact such as liquid carbonic. In the absence of such arecycling unit 60, the cooling fluid withdrawn by the vacuum unit 56 isdischarged into the atmosphere.

As shown in FIG. 2, the receiver frame 30 is defined by a plurality ofperimeter plates 62 which cooperate to define the overall geometry ofthe receiver unit 30. A vacuum plenum 64 is provided at the rear of thereceiver unit and is coupled to the flexible conduit 58 discussedpreviously. The chamber elements 32 are each coupled by a threadedelement 66 to the vacuum plenum. Each of the chamber elements is seen toconstitute a generally cylindrical wall member 68 extending forward fromthe threaded element 66 through an opening in front wall 70.

Each chamber element 32 includes an inwardly directed lip 72 at themouth of the cylindrical wall 68 adapted to engage the lower surface ofa radially extending flange 74 on parison 76 so as to suspend theparison within the chamber element 32 such that a small space isprovided between the outer wall 78 of parison 76 and the inner surface80 of wall member 68. A plurality of openings 82 on the front face 86 ofthe chamber elements 32 provide a pathway for cooling fluid to enter thespace between the parison outer wall 78 and the chamber element innerwall 80. The openings 82 are shown in FIG. 2 as holes but can also beinclined slots as shown in FIG. 4o A seal in the form of groove 84surrounds the plurality of openings 82 on the front face 86 of thechamber elements 32.

A cooling head 46, shown in greater detail in FIG. 3, is coupled toconduit 44 which supplies cooling fluid from source 42 shown in FIG. 1to a pressure plenum 88. The cooling head 46 includes a plurality ofstem elements 90 which are adapted to project into the interior of theparison 76. The stem elements 90 include a plurality of small apertures92 through which cooling fluid passes to cool the interior surface ofthe parison. The cooling fluid passes from the pressure plenum 88 intothe stem elements 90 through hollow threaded element 94 which elementalso secures a cap unit 96 enclosing a finish receiving chamber 108 tothe forward plate 98 of the pressure plenum 88. The lip 110 of the capunit 96 includes a sealing means such as O-ring 112 to seal the finishreceiving chamber 108 to the front face of the corresponding chamberelement 32.

FIG. 4 shows an alternative embodiment for the receiver unit 30 whereinat least one of the chamber elements 32 includes a heat sensor 33 forsensing the temperature of the parison 76. A cable 35 couples the heatsensor 33 to the cooling program controller 55 to provide the controller55 with information concerning the parison temperature. The heat sensor33 is preferably a non-contact infrared heat sensor having a very lowthermal inertia which permits the sensor to reflect quick changes intemperature. The cap unit 96 of the cooling head 46 is shown to includea sleeve portion 100 which slips over the outer surface of thecylindrical wall member 68 of the receiver unit 30. The close fitbetween the sleeve portion 100 and the cylindrical wall member 68defines a seal preventing unwanted discharge of the cooling gas to theenvironment.

In use, a set of molded parisons 76 or other similar work pieces formedin an injection molding machine 10 are received by a receiver 30 uponbeing stripped from cores 20 by a stripper mechanism 26. The receiver 30is transported from a position within the molding machine 20 to a secondposition adjacent to the molding machine by a transporter mechanismfollowing a pathway 34. A cooling head 46 moves along a path 48perpendicular to pathway 34 to engage, and be sealed to the receiverframe 30 such that stem elements 90 project down into the interior ofthe parison 76 which are retained within the hollow cylindrical walls 68of the chamber elements 32. Sensor 52 then activates the programcontroller 55 which controls the release of a cooling fluid such asliquid nitrogen or liquid carbonic from source 42 through conduit 44into pressure plenum 88 where the liquid is warmed sufficiently tochange state to a gas at about the temperature of the liquid.

The gas then is distributed through openings 92 in stem 90 to theinterior and top of the parison 76. The cooling gas, prevented fromescaping into the atmosphere by seal means 112, travels through openings82 through the space between the outer wall 78 of the parison 76 and theinner wall 80 of the chamber elements 32 to further cool the exterior ofthe parison 76. Subsequent to contact with the walls of the parison 76,the cooling fluid is drawn into vacuum plenum 64 through hollow threadedmember 66 by vacuum unit 56. The cooling fluid can then be recycledthrough the filtering and chilling unit 60 back to the source of coolingfluid 42.

Following the cooling of the parisons, the cooling head 46 retracts tothe position shown in FIG. 1 and the receiver means is pivoted bydischarge unit 38 in the direction of arrow "C" to discharge the cooledparisons onto moving conveyer belt 40 or other similar product handlingdevice. During the cooling process, the injection molding machine 10 hasexecuted another molding cycle. Upon return of the receiver frame to thevertical position shown in FIG. 1, receiver frame is carried into thespace between the cavity unit 18 and stripper frame 26 to receiveanother set of parisons.

The cooling program controller 55 permits one to apply cooling fluidduring any portion of the time during which the position sensor 52indicates that the receiver unit 30 and cooling head 46 are engaged. Thecontroller 55 also permits one to selectively apply a discontinuous flowof cooling fluid to the parison. The discontinuous flow is preferablyapplied as a succession of bursts of cooling fluid interspersed withperiods of no flow. The advantages to be gained by such a discontinuousapplication of cooling fluid are shown by the following table. The tablerecords the final measured temperature of parisons having an initialmold exit temperature of 250° F. when subjected to different patterns ofcooling fluid application. In each Example liquid nitrogen at atemperature of -300° F. was introduced into the pressure plenum 88 atthe same pressure for the periods of time indicated by the word "ON". Ineach Example the vacuum was applied to the receiver during the entire 8seconds that the receiver and cooling head were engaged.

    ______________________________________                                 FINAL TEM-    EXAMPLE   FLOW TIME (SEC.)   PERATURE    ______________________________________    EXAMPLE   ON               51/2            140° F.    A(comp.)  OFF    1/2               2    EXAMPLE   ON           21/2        21/2    127° F.    B         OFF    1/2           11/2    1    EXAMPLE   ON           11/2    11/2    11/2                                               110° F.    C         OFF    1/2       11/2    11/2    ______________________________________

In comparative Example A the cooling fluid was applied as a continuousflow for 51/2 seconds in accordance with the earlier embodiment of thepresent invention as disclosed in U.S. Pat. No. 5,114,327. In workingExamples B and C, the cooling fluid was applied as a discontinuous flow;that is, the flow of cooling fluid was interrupted at least once duringthe total cooling period of eight seconds. While the total time ofresidence of the preforms in the receiver was the same in each of theExamples, the total flow time for the cooling fluid was reduced to 5seconds in Example B and 41/2 seconds in Example C. The surprisingresult achieved by the present invention is that more cooling of thepreform was achieved with less total cooling fluid when the fluid isapplied in short bursts rather than one long continuous flow. It will beappreciated by those skilled in the art that where, due to preformshape, weight or other factors, less cooling is needed, the "OFF" timecan be lengthened thereby achieving even additional savings for processcosts.

Although the invention has been described in detail with reference tothe illustrated preferred embodiment, variations and modifications existwithin the scope and spirit of the invention as described and is definedin the following claims.

What is claimed is:
 1. A method of rapidly cooling a set of moldedworkpieces formed in an injection molding machine, the method comprisingthe steps of:receiving said molded workpieces upon ejection from saidmolding machine on a receiver means; transporting the receiver meansrelative to said molding machine between a first position within saidinjection molding machine and a second position adjacent to saidinjection molding machine; providing a source of cooling fluid anddirecting means for directing the cooling fluid toward a surface of eachworkpiece in the receiver means; moving the directing means relative tothe receiver means between an engaged position where the directing meansand receiver means are engaged with each other and a disengaged positionwhere the directing means and receiver means are spaced from each otherby a minimum distance; and selectively supplying a discontinuous flow ofthe cooling fluid from said source to the directing means when thedirecting means is engaged with the receiver means.
 2. The method ofclaim 1 wherein the selectively supplying step further comprises thesteps of sensing the relative position of the receiver means and thedirecting means, and allowing said discontinuous flow of the coolingfluid through the directing means toward said workpieces only when thereceiver means and the directing means are contiguous to each other. 3.The method of claim 2 further comprising the step of recycling thewithdrawn cooling fluid through a cooler to permit reuse of the coolingfluid.
 4. The method of claim 2 wherein the receiving step furthercomprises the step of positioning an outside surface of said workpiecesin spaced-apart relation from the receiver means to allow cooling fluidto contact said outside surface of the workpieces.
 5. The method ofclaim 2 further comprising the step of discharging the workpieces fromthe receiver means subsequent to cooling of the workpieces by thecooling fluid.
 6. The method of claim 5 wherein the discharging stepfurther comprises the step of rotating the receiver means through anangle sufficient to cause said workpieces to be dumped from the receivermeans.
 7. The method of claim 2 further comprising the step ofinhibiting the escape of cooling fluid into the atmosphere.
 8. Themethod of claim 7 further comprising the step of withdrawing coolingfluid from the receiver means subsequent to contact between theworkpieces and the cooling fluid.